nevermind this patch, it fails:

llvm[1]: ***** Completed Release+Debug+Asserts Build
make[1]: Leaving directory '/home/zazdxscf/build/1nonpkgs/rust/rust/x86_64-unknown-linux-gnu/llvm'
touch /home/zazdxscf/build/1nonpkgs/rust/rust/x86_64-unknown-linux-gnu/llvm/Release+Asserts/bin/llvm-config
touch: cannot touch ‘/home/zazdxscf/build/1nonpkgs/rust/rust/x86_64-unknown-linux-gnu/llvm/Release+Asserts/bin/llvm-config’: No such file or directory
/home/zazdxscf/build/1nonpkgs/rust/rust/mk/llvm.mk:89: recipe for target '/home/zazdxscf/build/1nonpkgs/rust/rust/x86_64-unknown-linux-gnu/llvm/Release+Asserts/bin/llvm-config' failed
make: *** [/home/zazdxscf/build/1nonpkgs/rust/rust/x86_64-unknown-linux-gnu/llvm/Release+Asserts/bin/llvm-config] Error 1

real  36m36.662s
user  108m0.769s
sys 10m35.750s

diff --git a/configure b/configure
index 60d3661..6b522c8 100755
--- a/configure
+++ b/configure
@@ -1448,12 +1484,12 @@ do
         LLVM_BUILD_DIR=${CFG_BUILD_DIR}$t/llvm
         if [ -n "$CFG_DISABLE_OPTIMIZE_LLVM" ]
         then
-            LLVM_DBG_OPTS="--enable-debug-symbols --disable-optimized"
+            LLVM_DBG_OPTS="--enable-debug-symbols --disable-optimized --enable-debug-runtime"
             # Just use LLVM straight from its build directory to
             # avoid 'make install' time
             LLVM_INST_DIR=$LLVM_BUILD_DIR/Debug
         else
-            LLVM_DBG_OPTS="--enable-optimized"
+            LLVM_DBG_OPTS="--enable-optimized --enable-debug-runtime --enable-debug-symbols"
             LLVM_INST_DIR=$LLVM_BUILD_DIR/Release
         fi
         if [ -z "$CFG_ENABLE_LLVM_ASSERTIONS" ]
